Piezoelectric voltage generator

ABSTRACT

A piezoelectric device is fitted with a hydraulic piston for exerting a loading thereon. The piston is periodically driven by a fluidic actuator thereby to repeatedly stress the piezoelectric crystal and produce an electrical voltage which may be used in a spark ignition circuit. The piezoelectric device, in combination with an internal combustion engine provides for automatic ignition and re-ignition in the event of an interrupted combustion process.

United States Patent Burge, Jr. et al.

1 1 PIEZOELECTRIC VOLTAGE GENERATOR Inventors: Harland L. Burge, Jr., Tarzana;

Richard J. Salvinski, Hacienda Heights, both of Calif.

Assignee: TRW lnc., Redondo Beach, Calif.

Filed: Sept. 4, 1973 Appl. No.: 393,874

U.S. Cl. 431/255, 310/8.7 Int. Cl. F23q 3/00, F02p 3/12 Field of Search 431/255; BIO/8.3, 8.6.

BIO/8.7; 137/815 References Cited UNITED STATES PATENTS 10/1967 Hodgson 431/255 X 7/1970 Rubin 137/8115 451 Feb. 11,1975

Kreuter i. 431/255 X Alibert et al 310/81 Primary Examiner-Edward G. Favors Attorney, Agent, or FirmWilliam B. Leach; Harry 1 Jacobs [57] ABSTRACT A piezoelectric device is fitted with a hydraulic piston for exerting a loading thereon. The piston is periodically driven by a fluidic actuator thereby to repeatedly stress the piezoelectric crystal and produce an electrical voltage which may be used in a spark ignition circuit. The piezoelectric device, in combination with an internal combustion engine provides for automatic ignition and re-ignition in the event of an interrupted combustion process.

4 Claims, 5 Drawing Figures IZ'JENTEU 1 5 SHEET 10F 3 Fig. 1

Fig. 2

PXJENTEBFEBI W5 2'. 865 539 SHEET 2 BF 3 OSCILLATOR Fig. 3

\; my aim Fig. 4

1 PIEZOELECTRIC VOLTAGE GENERATOR BACKGROUND OF THE INVENTION This invention relates to piezoelectric voltage generators in general and more specifically to propellant ignition systems.

It is known that certain crystals, when deformed or stressed, develop an electric field referred to as the pi ezoelectric effect. The deformation is usually very small, but the associated mechanical force may be very large.

A typical piezoelectric igniter system is represented by the US. Fat. to Riverson, No. 4,603,710 which discloses a piezoelectric igniter for a hand held cigarette lighter. The stress producing means includes a slideable piston acting under the influence of gravity or acceleration forces.

While devices of this type are very satisfactory for many applications, they nevertheless suffer from shortcomings in applications such as rocket motors.

Accordingly, it is an object of this invention to provide a piezoelectric voltage generator not subject to the shortcomings and disadvantages of the prior art.

It is another object of the present invention to provide a piezoelectric voltage generator that utilizes a pressurized gas, such as rocket propellant, in the stress producing mechanism.

It is a further object of the present invention to provide a piezoelectric voltage generator wherein the crys tail is repeatedly stressed at a high rate.

SUMMARY OF THE INVENTION In accordance with the teachings of the invention a piston is mounted in a housing and a piezoelectric device is mounted in relationship to the piston so as to stress the piezoelectric device upon a relatively small movement of the piston. The piston movement is actuated by fluid pressure supplied to the piston chamber through a fluidic oscillating circuit. Either impact and non-impact stress loading may be utilized.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a fluidic oscillating circuit and a portion of a piezoelectric assembly in ac cordance with the invention;

FIG. 2 is a schematic diagram ofa non-impact piezoelectric assembly used in conjunction with the fluidic oscillating circuit of FIG. 1',

FIG. 3 is an alternative piezoelectric assembly of the impact type;

FIG. 4 is a particular embodiment of a piezoelectric voltage generator; and

FIG. 5 is a schematic diagram of a piezoelectric assembly as shown in FIGS. 1 4 in a rocket motor systern.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 there is shown a fluidic oscil lator circuit I0 suitable for periodically actuating movement of a stress loading piston as herein further explained. A fluid, such as gaseous air, nitrogen, hydrogen or other gas, is supplied under pressure to the cir cuit inlet 11 whereupon the fluid may flow through either of two paths I2, 22. One path 12 leads to one 'portion of the fluidic circuit herein denoted as a first fluidic device or digital amplifier 13 which has two outlets I4, 15. One outlet I4 is coupled to the piston chamber M of a piezoelectric assembly 30 which includes a piezoelectric device 32 and a piston 33, the operation of which will be explained below. The digital amplifier 13 also includes control ports l6, 17. When pressure is supplied to control port 17, the fluid flow is caused to exit through outlet 14. When pressure is depleted at port I7 and supplied to control port I6, the fluid flow is caused to flip to the other outlet I5. Thus, if control pressure is alternately supplied to control ports I6, I7, the fluid flow is caused to alternately flip from one outlet I4, to another 15.

The other inlet fluid path 22 is coupled to a second fluidic device, or flip-flop, 23 also having two outlets 24, 25 and two control ports 26, 27. It may be seen from FIG. I, that when fluid flows through outlet 14 of the amplifier l3, fluid will also be flowing through outlet 24 of the flip-flop 23 thereby supplying pressure to control port 17. The digital amplifier is designed to be used as a power amplifier device. Thus, fluid logic devices operating at low supply pressures can provide control signals for the higher flow and higher pressure output of the digital amplifier.

Fluid in the piston chamber 31 is permitted to exit through a fluid return path I8 thereby supplying pressure to control port 27. This then causes fluid to exit from the flip-flop 23 through outlet 24 which supplies pressure to the digital amplifier control port I6 causing fluid to exit the flip-flop through outlet 15. The pres sure in piston chamber 3I therefore decays permitting the relief of stress on the piezoelectric device 32.

Further study of FIG. 1 shows that pressure supplied by outlet IS to control port 26 flips the fluid flow to outlet 25, control port 17, and thus, fluid flow is flipped to again enter the piston chamber 31. A fluidic circuit of the type shown in FIG. I has vents sized and located to allow the pressure to decay within a selected time period after the fluid source has been flipped to a different path. Vents are schematically shown and identified by numeral I9 in FIG. I.

It will be immediately apparent to one familiar with the fluidic art that the operation of the oscillating circuit of FIG. I is dependent upon the proper selection of flow path resistance and capacitance as well as supply pressure. To this end, an accumulator or capacitance cavity 28 is included to provide additional control over the circuit frequency characteristics. The circuit of FIG. I is merely an example of one circuit having acceptable operating characteristics and was assembled with commercially available components, thus the circuit of FIG. I is not purported to be an optimum circuit.

Turning now to FIG. 2 there is shown one embodiment of a non-impact piezoelectric assembly 30. The assembly includes a piston 33 mounted in a housing 34 by flexural members 35 which permit small movements of the piston. One pair of piezoelectric devices 32 are mounted between the piston 33 and one endwall 36 of the housing 34 which in this embodiment is a bias member providing prestressing of the piezoelectric device. In accordance with well known piezoelectric technology, an electrical potential will occur across leads 37 when the piezoelectric devices 32 undergo stress forces caused by small movements of the piston 33.

Also shown in FIG. 2 is an inlet 14a which when coupled to the outlet I4 of the fluidic oscillating circuit of FIG. I provides means for periodically moving the piston 33 away from the piezoelectric devices 32 to thereby relieve the prestressed condition. A vent port 18a may be coupled to return path 18 of the fluidic oscillator.

As further shown in FIG. 2, a second chamber 310 may be included as well as a second pair of piezoelectric devices 32a having electrode leads 37a and which also are prestressed by a second bias member 360. The actuation of the piston 33 may be augmented by coupling the second chamber 31a into the fluidic circuit. This may be implemented by substituting the second chamber 310 for the accumulator cavity 28 of FIG. 1. Thus, an inlet b to the second chamber 31a is provided which is coupled to outlet 15 of FIG. 1, and an outlet 2615 from the second chamber 310 is coupled to the control port 26 of FIG. 1. While a piezoelectric assembly may be constructed having a single piezoelectric crystal element, the use of at lest a pair of elements as at 32 is a convenient means of providing an increased potential for a given piston deflection.

HO. 3 shows an embodiment of the invention in the form of an impact type of device. This embodiment, like that of FIG. 2 is a two chamber device coupled to the fluidic oscillator. The piezoelectric devices 32, 32a are each spaced from the piston 33. As shown the spacing is exaggerated for clarity, and in application would be in the order of 0.25 inches. In addition to the features already described in conjunction with FIG. 2, there may be included a bias member 40 in place of the fluidic pressure to the second chamber 31a. Thus, fluidic pressure drives the piston toward piezoelectric device 32a impacting therewith and upon venting of the pressure in the first chamber 31, the bias member 40 drives the piston into impact with the first piezoelectric devices 32. As a feature of implementation. the housing 34 is grounded at 41.

A design that was constructed for research and development purposes is shown in FIG. 4. The purchased fluidic devices l3, 14 were mounted on a fluidic logic body 45 having formed therein the various interconnecting fluid passageways of which outlets l4, 15 of the digital amplifier 13 are indicated. Outlet 14 leads to the chamber 31 for activation of the piston 33 which engages a copper terminal 46. This terminal in turn engages one end of the piezoelectric device 32. An insulation body 47 supports the piezoelectric devices 32 in housing 34. This embodiment used an O-ring seal instead of flexure elements to support the piston and further support for the piston is providedi by ring member The voltage generator of FIG. 4, shown substantially to scale, utilized a piston 1.75 inches in diameter. Both gaseous nitrogen and gaseous helium with pressure up to 400 psig were used to drive the fluidic oscillator. The fluidic circuit was permissive of piston actuation at the rate of 50-60 cycles per second and output peak voltages measured up to approximately 7,000 volts.

A piezoelectric voltage generator as herein described may be made without any moving parts if the piston is flexure mounted. As a means for spark ignition in propulsion devices having propellant delivered to the combustion chamber under pressure, the propellant may be used to operate the fluidic oscillator. Thus, a rocket motor ignition system may be provided which is entirely automatic in operation and which would reinstate operation in the event of combustion failure or flameout. Similar ignition systems may be devised for commercial and home furnaces and similar systems subject to flame-out. While the voltage generator as described has been discussed in terms of a gaseous fluid, liquid operating systems may also be designed in accordance with these teachings and in accordance with fluidic hardware technology.

As shown in FIG. 5, a rocket motor is supplied with a fuel reactant from a fuel source 51 through a fuel line 52 and a fuel engine start valve 53. Similarly, an oxidizer reactant is supplied from an oxidizer source 55 through an oxidizer line 56 and an oxidizer engine start valve 57. The reactants may be in a gaseous state under pressure or may be pressurized by a separate pressurizing tank in a conventional manner. The reactants are thereby supplied to the rocket motor under pressure and are introduced through the usual injector device.

A fluidic oscillator-piezoelectric assembly 60 of the type herein described may be supplied with a high pressure fluid by coupling one of the reactant supply lines, such as the fuel line 52, to the fluidic oscillator inlet as by line 61. The electrode terminal 32 of the assembly is coupled to a spark-ignition device 62. The fluidic oscillator output 18 may be directed to any convenient disposal but, in particular, it may be coupled into the combustion chamber of the rocket motor. In most cases, it is necessary to use parallel reactant circuits, one directed to the rocket motor and one to the fluid oscillator inlet, but in some applications it may be feasible due to flow requirements to direct the entire reactant flow through the fluidic circuit and then into the rocket motor. The utilization of the fluidic circuit in combination with the piezoelectric device as a voltage generator enables the use of one of the reactants as the voltage generator driving force. In this manner, the ignition system is both simple and reliable providing for automatic ignition upon opening of the engine start valves and providing automatically for reignition in the case ofa flame-out. Furthermore, the system is particularly safe because the ignition source is not a separately initiating system subject to its own initiation failure.

What is claimed is:

l. A combustion system of the type having a reactant injector, a source of a reactant at a high pressure, means for supplying the reactant to the injector and a spark ignition device in communication with the combustion zone, and comprising:

a housing;

a piston moveably mounted within said housing, said housing, and one end surface of said piston defining a first chamber therebetween',

a piezoelectric device mounted within said housing and positioned in engageable relationship with the other end surface of said piston for producing an electrical potential when subjected to mechanical stresses induced therein upon movement of said piston toward said device, said device including electrode terminals coupled to the combustion system ignition device; and

a fluidic oscillator coupled to said chamber and to the reactant source, the one surface area off said piston being greater than the area of engagement of the other surface with said piezoelectric device by a factor of at least ten whereby reactant, when supplied under pressure to said oscillator, is periodically introduced into and relieved from said chamber for actuating periodic movement of said piston 6 and producing an alternating voltage across said whereby fluid, when supplied under pressure to terminals and to the ignition device. said oscillator, is periodically introduced into said 2. A piezoelectric voltage generator comprising: first chamber for actuating movement of said piston and producing a voltage across said terminals.

a housing; a piston moveably mounted within said housing, said 5 3. The piezoelectric voltage generator of claim 2 furhousing and said piston defining first and second ther comprising: chambers therebetween; a flexure member interconnecting said piston and a first piezoelectric device mounted within said first said housing for permitting movement of said pischamber and having electrode terminals for outton. puting a voltage therefrom. to 4. The piezoelectric voltage generator of claim 2 fura second piezoelectric device mounted within said ther comprising:

second chamber and having electrode terminals for means coupling said second chamber and said fluidic outputing a voltage therefrom, each of said piezooscillator circuit and alternatingly pressuring said electric devices positioned to have stresses induced chambers when fluid is supplied under pressure to therein upon movement of said piston; said fluidic oscillator.

a fluidic oscillator coupled to said first chamber Lil 

1. A combustion system of the type having a reactant injector, a source of a reactant at a high pressure, means for supplying the reactant to the injector and a spark ignition device in communication with the combustion zone, and comprising: a housing; a piston moveably mounted within said housing, said housing, and one end surface of said piston defining a first chamber therebetween; a piezoelectric device mounted within said housing and positioned in engageable relationship with the other end surface of said piston for producing an electrical potential when subjected to mechanical stresses induced therein upon movement of said piston toward said device, said device including electrode terminals coupled to the combustion system ignition device; and a fluidic oscillator coupled to said chamber and to the reactant source, the one surface area off said piston being greater than the area of engagement of the other surface with said piezoelectric device by a factor of at least ten whereby reactant, when supplied under pressure to said oscillator, is periodically introduced into and relieved from said chamber for actuating periodic movement of said piston and producing an alternating voltage across said terminals and to the ignition device.
 2. A piezoelectric voltage generator comprising: a housing; a piston moveably mounted within said housing, said housing and said piston defining first and second chambers therebetween; a first piezoelectric device mounted within said first chamber and having electrode terminals for outputing a voltage therefrom; a second piezoelectric device mounted within said second chamber and having electrode terminals for outputing a voltage therefrom, each of said piezoelectric devices positioned to have stresses induced therein upon movement of said piston; a fluidic oscillator coupled to said first chamber whereby fluid, when supplied under pressure to said oscillator, is periodically introduced into said first chamber for actuating movement of said piston and producing a voltage across said terminals.
 3. The piezoelectric voltage generator of claim 2 further comprising: a flexure member interconnecting said piston and said housing for permitting movement of said piston.
 4. The piezoelectric voltage generator of claim 2 further comprising: means coupling said second chamber and said fluidic oscillator circuit and alternatingly pressuring said chambers when fluid is supplied under pressure to said fluidic oscillator. 